Protection of relief valves



Patented Apr. 18, 1944 UNITED STATEfii OFFICE PROTECTION OF RELIEF VALVES Elza Q. Camp, Goose Creek, Tex., assignor to Standard Oil Development Company, a corporation of Delaware 6 Claims.

In many operations it is essential to maintain corrosive gases under pressure in a vessel and to provide the vessel with means for relieving excess pressure by means of a relief vent pipe.

The present invention is directed to a means for reducing or eliminating corrosion and failure due to corrosion of pressure relief valves used on pressure vessels.

The present invention has been found particularly suitable to the operation of flue gas generators used for producing flue gases under a normal pressure of approximately 250 pounds per square inch. The air and fuel gas are admitted to the flue gas generator in the ratio in which they are required for complete combustion. The moisture and acidic constituents present in the flue gas are very corrosive. Accordingly, difficulty has been encountered in providing a pres-- sure relief system which will operate satisfactorily in emergencies and not require constant maintenance because of the corrosive action of the gases.

Other objects and advantages of the present invention may be seen from a reading of the following description taken from the drawing in which the three figures represent three different embodiments which have been found suitable for practicing the present invention.

Figure I is a diagrammatic representation of one embodiment of this invention applied to a flue gas generator; 1

Figure II is a diagrammatic representation of another embodiment of the invention; and

Figure III is a diagrammatic representation of still another embodiment of the invention.

Referring specifically to the drawing and first to Figure I, flue gas generator H is provided with burners 52 which are connected to a source of fuel gas 13 and air M. The products of combustion are removed from the generator via conduit l5. This apparatus is conventional to the art. To relieve pressure resulting from an explosion Within the flue gas generator, a vent pipe I6 is connected to the generator close to the burner and is provided with suitable means for relieving excess pressure. In the embodiment shown, a frangible disk I! is inserted in the vent line, the disk being machined so that it will rupture when it is subjected to a predetermined pressure. In practice it has been found convenient to operate the flue gas generator at a pressure of approximately 250 pounds per square inch and to provide a frangible disk which will rupture upon a pressure difierential of 550 to 750 pounds per square inch, depending on the temperatures under which operations are conducted. For example, at about 250 F., the disk is designed to rupture at about 610 pounds per square inch.

In accordance with the present invention the frangible disk is protected from corrosion by the insertion of a second disk H3 in the vent line it between the flue gas generator and disk ll. and inert gas is forced into the space defined by the two disks to equalize the pressure on disk l8. Disk it is made to withstand only a very small ressure differential and is provided simply to insure that no corrosive gases will be allowed to come in contact with the frangible disk ll. For example. whereas the disk ii is commonly constructed to withstand a differential pressure of 550 to 750 pounds per square inch, disk it will. rupture at pressures no greater than 20 pounds per square inch or of the order of magnitude of about one twenty-fifth the pressure disk ll will withstand.

The inert gas used in the embodiments disclosed in Figure I will fill the space between disks H and Hi. It is provided by drawing oiT flue gas from vent it at a point below disk it by line E9, passing it through vessel in containing caustic or sodium carbonate or other similar basic material to remove acidic constituents, then through vessel 2i filled with a drying agent, such as calcium chloride, alumina, etc, and subse quently returning the gas to vent line 56 at point between disks ii and it by a line 22. It will be evident that slight fluctuations of pressure within flue gas generator ii are almost immediately equalized on both sides of disk 23. Whereas, a pitting of frangible disk il, which is maintained under considerable stress, will. cause the rapid failure of the disk, the equalization of pressure on both sides of disk 88 allows it to be in service with one side in contact with corrosive gases for a substantial period of time before failure occurs. In like manner the scrubbing of the gas to remove moisture and acid before it is allowed to come in contact with frangible disk .7! allows this member to be placed under considerable stress for extended periods of time before failure occurs.

Another embodiment for practicing the present invention is illustrated in Figure II in which like parts are given the corresponding numbers as in the preceding figure. In this embodiment line 25 connects the lower portion of vessel 26 with vent l6 and connecting into line 25 is a line 26 used for bleeding air into the system. A small amount of air is continually bled into the system by line 25 so that normal fluctuation of pressure of the flue gas generator will not draw acidic materials into scrubber 29. It will be understood that substantial changes in pressure in the flue gas generator will force flue gas from vessel H to scrubber 2% but ordinarily the bleeding of air into line 25 will keep scrubber 29 free of acidic materials and substantially prolong the life of the packing thereof.

Another embodiment suitable for the practice of the present invention is shown in Figure III. In this embodiment a line 38 is connected with a source of compressed air, now shown, at a pressure higher than that in the flue gas generator. Line 33 divides into two branches. Branch 3i connects into vent it below disk it and branch 32 connects into vent l 6 at a point between disks l8 and H. It is desirable to inject substantial amounts of air into the system by line at so that any fluctuation in pressure within generator M will simply compress air in line 32 rather than allow the passage of acid and moisture containing material from the generator by a line 3! and 32 into the space adjacent to disk H. The arrangement shown in this figure allows both oxygen and moisture to come into contact with the high pressure side of the frangible disk ll. Accordingly, the life of disk I? is not as great when employing this modification as when employing the modifications shown in the preceding figures. However, the elimination of scrubbers 2i 2! and the necessity of periodically repacking them, at least in some measure compensates for the shortened life of disk l'l.

As an example of the advantages enjoyed when practicing the present invention, a flue gas generator with a capacity of from 15,003 to 29,090 cubic feet per hour was constructed with two Vent lines, each controlled by a frangible disk approximately 10 inches in diameter. In addition to the products of combustion of the fuel gas and air, substantial amounts of gas were recycled to the generator from the catalytic reactor of a hydroforming unit so that the gas in the generator contained substantial amounts of sulfuric acid, sulphur dioxide, hydrochloric acid, free sulphur and moisture. The frangible disk I? maintained under a tension of 250 pounds per square inch and exposed to the highly corrosive gases had a life no greater than five days. An attempt was made to prolong the life of disk if by inserting an orifice plate between the disk l! and the generator and purging the space between the frangible disk and orifice plate with inert gas. This arrangement did not prolong the life of the frangible disk to any appreciable amount. It is believed that the reason this arrangement did not give better results was due to the pressure fluctuations within the flue gas generator which allowed acidic material to come into contact with the frangible plate. The apparatus shown in Figure II was installed and the device supplied with scrubbed gases in the space between disk i8 and frangible disk ll. This arrangement so increased the life or the frangible disk I"? that operation of the generator was continued 80 days without its failure.

While I have disclosed specific embodiments suitable for practicing my invention, it will be obvious that changes may be made in the apparatus above described and in the procedure followed without involving invention, For example,

instead of using, two scrubbers in Figures I and II, a single scrubber may be substituted therefor and alternatively more than two scrubbers may be employed. Likewise instead of using a frangible disk as the pressure relief means, other suitable arrangements such as a spring loaded valve or weight loaded valve may be used.

I claim:

1. A means for protecting a pressure relief means in fluid communication with a pressure vessel containing corrosive fluid under a fluctuating pressure by a passage, comprising a membrane sealing the passage between the pressure vessel and the pressure relief means, a conduit connecting the space defined by the membrane and the pressure relief means with the pressure vessel, and a means in fluid communication with said conduit arranged for supplying non-corrosive gas to said space.

2. A device in accordance with claim 1 in which a scrubbing means is inserted in the conduit between said space and said pressure vessel.

3. A device in accordance with claim 1 in which a scrubber is arranged in the conduit and a source of inert gas fluidly connects to said conduit at a point between said pressure vessel and said scrubher.

4. A device for protecting a pressure relief means in fluid communication with a pressure 39 vessel containing corrosive fluid under a fluctuating pressure by a passage, comprising a membrane sealing the passage between the pressure vessel and the pressure relief means, a scrubbing means having an outlet and an inlet and adapted to remove moisture and acidic constituents from a gas, a first conduit connecting the pressure vessel with the inlet of said scrubbing means and a second conduit connecting the outlet of said scrubbing means with the space defined by the 40 membrane and the pressure relief means.

5. A device for protecting a pressure relief means in fluid communication with a pressure vessel containing corrosive fluid under a fluctuating pressure by a passage, comprising a membrane sealing the passage between the pressure vessel and the pressure relief means, a scrubbing means provided with an inlet and an outlet and adapted to remove moisture and acidic constituents from a gas, a first conduit in communication vessel and the pressure relief means, and a con-' duit in communication with a source of highpressure air provided with at least two relatively short branches, with one of said branches fluidly connected to said high-pressure vessel and the other branch fluidly connected to the space defined by said membrane and said pressure relief means.

ELZA Q. CAMP.

with a source of compressed air connecting the i 

